1. Field of the Invention
The present invention relates to a cross-sectional profile measuring method.
2. Description of Related Art
In order to measure a profile of an object, a coordinate measuring machine has been typically used. A contact probe of the coordinate measuring machine is brought into contact with a surface of the object for scanning to obtain measuring data of the profile of the object.
For instance, Patent Literature 1 (JP-T-2009-531695) discloses that a five-axis control coordinate measuring machine with a probe whose stylus posture can be adjustable arbitrarily is used for measuring a cross-sectional profile of a turbine blade. Surface profile data is obtained by moving the stylus along a surface of the object in a serpentine manner or continuous cross-sectional profile data is obtained by circularly moving the stylus along the circumference of the object.
A plurality of cross-sectional profiles need to be measured for many objects. For instance, for an object such as a turbine blade having blade profiles gradually changing in the longitudinal direction thereof, it is necessary to accurately measure cross-sectional profiles at plural sections shifted in the longitudinal direction at predetermined intervals.
In this case, generally, one part program, which is composed for circularly moving the stylus around an object for measuring the cross-sectional profile and provided for each section to be measured, is executed at the corresponding section. Each time when the section to be measured is changed, the stylus is necessarily brought into contact, moved for measurement, removed from the object, and moved to a different section. The probe has to be accelerated or decelerated for each of the above actions, so that operating efficiency is lowered.
In contrast, according to Patent Literature 2 (JP-A-2009-293992), in order to continuously measure cross-sectional profiles of an object at plural sections, after being brought into contact with the object for cross-sectional profile measurement at a predetermined section, the stylus is moved to the next section while being in contact with the object, and then performs the cross-sectional profile measurement at that section. When a series of cross-sectional profile measurement is completed by repeating the above process, the stylus is removed from the object.
In Patent Literature 2, measurement-start points (measurement-end points) are simply shifted from one another in the longitudinal direction of the object. Additionally, the operation of the probe for measurement, i.e., the circular movement of the stylus around the object, is the same irrespective of the measurement sections.
In order to measure a cylindrical object, the stylus is not circularly moved around the object at each of plural sections but may be moved along a spiral locus for measuring the surface profile of the object. When the stylus is moved along the spiral locus, the probe can continuously perform the measuring operation, so that a measurement state can be uniformed during the measuring operation (e.g., the stylus can be moved at a constant speed). Patent Literature 3 (JP-T-2009-501321) discloses such a spiral profile measurement. Additionally, in order to stabilize the measurement data, a pre-scanning path (an acceleration range) and a post-scanning path (a deceleration range) are provided before and after the measuring operation so that the measuring operation can be stably performed during the spiral movement of the stylus through a range between the pre-scanning path and the post-scanning path.
Although the technique of providing the acceleration range and the deceleration range as disclosed in Patent Literature 3 is effective in stabilization of measurement data, this technique cannot be simply combined with the continuous measurement for measuring plural cross-sectional profiles as disclosed in Patent Literature 2.
In other words, in the cross-sectional profile measurement as disclosed in Patent Literature 2, although the stylus is kept in contact with the surface of the object for continuous measurement, the measurement section has to be changed after the measuring operation of the probe (i.e., the circular movement of the stylus around the object). In view of the above, it is not effective to accelerate and decelerate the probe before and after a series of measuring operation.
According to Patent Literature 3, although the profile can be stably measured by accelerating and decelerating the probe before and after the measuring operation, the stylus has to be moved along the spiral locus and thus it is not possible to directly measure plural cross-sectional profiles. As a result, a complicated calculation or the like is necessary to obtain the plural cross-sectional profiles.